1. Field of the Invention
This invention lies in the field of self-acting denture cleansing tablets.
2. Prior Art
Cleansing tablets for an automatic or self-acting cleansing of dentures in an aqueous solution containing initially sodium bicarbonate functioning as a gas-forming component, sodium polyphosphates as lime bonding agents, additional organic calcium bonding agents and acid carriers, caroates as oxidizing agents, surfactants in the form of alkyl- or alkyl-aryl sulfonates (such as alkyl benzene sulfonates), and carrier agents and release (or parting) agents, are described, for example in the Austrian Letters Pat. No. 264,015. In use, such a conventional tablet is simultaneously placed in water with the dentures, or the like, which are to be cleansed, herein briefly referred to as dentures, whereupon such cleansing tablet then disintegrates accompanied by a more or less strong development of gas, so that the solvent medium is strongly agitated, and the nascent, chemically active substances attack the coating formed on the dentures. In the case of these known cleansing tablets, all the effective agents and components go into solution virtually simultaneously.
Such a simultaneous dissolution of components is disadvantageous because different components of cleansing tablets of this type; for example, the oxidizing or the oxygen-active caroates (salts of Caro's acid), on the one hand, and the reducing citric acid, on the other hand, in part work against one another, so that the overall cleansing effect of the cleansing bath is diminished. Moreover, the comparatively rapid run-off (or cycle) of this monostage cleansing process has the disadvantage that some substances, such as, for example, the oxygen-active substances, particularly the caroates, have very little effect at the beginning of the dissolution process in the cleansing bath, because the pre-conditions necessary in order for them to be effective, such as softening of the water, cracking and partial demineralization of the coating by sodium polyphosphates, or perphosphates, have not yet been adequately realized. As a consequence, it is necessary to use a larger quantity of active agents in order to achieve a specific minimal effect required for the cleansing of dentures than would actually be necessary if there were an improved chronological control of a given denture cleansing operation. However, increasing the relative quantity of active agents in a cleansing tablet results in the disadvantage that, when the tablet is dissolved, the cleansing bath becomes comparatively viscous, as a consequence of which the destruction and dissolution of the coating is again negatively affected.
Even in the case of cleansing tablets whose compositions differ only very slightly from that of the cleansing tablet according to the Austrian Letters Pat. No. 264,015, such as, for example, the denture cleansing tablet described in the Austrian Letters Pat. No. 275,044 which contains a content of persulfates, phosphates, surfactants, aromatic substances, germicides, soda, and starch which is soluble in lime water, which agents additionally include a dye, erythromysin, and chelating agents, the cleansing process still proceeds in one stage. Although, with the aid of the chelating agents provided therein, it is possible to chronologically control the oxidative bleaching operation as can be determined by the change in color, this known cleansing tablet is also subject to the fundamental shortcoming consisting in that not all the effective agents are capable of attacking the denture coating in an optimum, chronological phasing. The same remarks apply to the tablets described in the U.S. Letters Pat. No. 3,337,466 wherein, with the aid of persulfates and per-compounds, at pH-values above 7, oxygen is developed, and which tablets contain phosphates, surfactants, and chelating agents, such as nitrilotriacetic acid and ethylene diamine tetraacetate, as well as a polyethylene glycol having a molecular weight of 6.000 as the binding agent for compression of the tablets. Although, as a consequence of the pH-value provided, which is over 7, the surfactants here, as in the case of the cleansing tablet according to the Austrian Letters Pat. No. 275,044, wherein the cleansing bath has a pH-value of 9.5 to 11.5, are capable of becoming more effective than in the case of the cleansing tablet of the generic type (Austrian Letters Pat. No. 264,015), wherein acidic solutions having pH-values of 1 to 5 are employed, there still exists the fundamental disadvantage in the case of all these tablets which is that oxygen-active, that is, oxidizing substances, on the one hand, and reducing (or deoxidizing), as well as surface-active substances, on the other hand, are not capable of attacking the denture coating in an optimal fashion.
In the German Offenlegungsschrift No. 2,357,720, a cleansing effect which is improved as compared with the previously known cleansing tablets has been achieved without necessitating an increase in the quantity of conventionally employed active agents by virtue of the fact that the initially cited cleansing tablet is subdivided into two layers of different composition. In the case of the cleansing tablet according to the German Offenlegungsschrift No. 2,357,720, of the initially cited substances present in the first and second layer, the sodium bicarbonate acts as a pH-stabilizing, gas-forming (or producing) carrier. The sodium hexametaphosphate acts as a softener, while, in the German Offenlegungsschrift No. 2,357,720, citric acid, provided as an organic calcium-binding agent, has a reducing, anti-microbial effect, and, in addition, dissolves the tartar present on the dentures to be cleansed. The ethylene diamine tetraacetate provided in the first layer has a softening and demineralizing effect, whereby, in addition, a tartar-dissolving effect can be observed. The high molecular weight polyethylene glycol used acts as an anti-microbial effervescent agent. The surfactants, as a whole, have an emulsifying effect, and decompose the denture coating by virtue of their surface-activity in the case of the cleansing tablet according to German Offenlegungsschrift No. 2,357,720. The cleansing tablet according to the German Offenlegungsschrift No. 2,357,720 also exhibits an organic calcium bonding agent in the second layer, namely, sodium citrate, which has the same effect therein as the citric acid in the composition of the first layer of the cleansing tablet according to the German Offenlegungsschrift No. 2,357,720. The sodium pyrophosphate has a reducing and softening effect, and decomposes the denture coating by means of surface action. The caroates employed (that is, the salts of Caro's acid), act as oxidizing agents. In the cleansing tablet according to the German Offenlegungsschrift No. 2,357,720, a conventional sodium salt of a polycarboxylic acid, such as is described in the German Offenlegungsschrift No. 2,357,720, page 7, lines 15 and 16, is provided as a polymeric dye carrier with a surface-active cleansing effect. This sodium salt, in the form of a surfactant, likewise improves the cleansing effect. The German Offenlegungsschrift No. 2,357,720 discloses sodium dodecyl benzene sulfonate, for example, as an alkyl benzene sulfonate utilizable as a surfactant, to which fatty acid-disodium sulfosuccinates can also be added. The preferred molecular weight of the polyethylene glycol employed amounts to 20,000 in the case of the cleansing tablet according to the German Offenlegungsschrift No. 2,357,720.
The cleansing tablet according to the German Offenlegungsschrift No. 2,357,720, due to its construction from two layers each of different composition, has the following effect: If the two-layer cleansing tablet according to the German Offenlegungsschrift No. 2,357,720 is placed in water together with the denture to be cleansed, the respective layers of different composition go into solution at greatly differing respective speeds, which is of particular significance in that only the second layer of the cleansing tablet according to the German Offenlegungsschrift No. 2,357,720 contains oxygen-active substances. The active and auxiliary agents of the described type of which the cleansing tablet according to the German Offenlegungsschrift No. 2,357,720 is constructed are thus introduced into the cleansing bath in a graduated (or step-wise) manner, as a result of which there is a greatly improved cleansing action as compared with the previously known tablets. It has been observed that the first layer is dissolved in approximately one to three minutes, and that the second layer is dissolved in approximately seven to ten minutes, in a tablet embodiment wherein each of the two layers extends from the two end faces of the tablet approximately to half the height of the whole tablet. Thus, from the beginning, the two layers of the cleansing tablet according to the German Offenlegungsschrift No. 2,357,720 have the same contact surface with the solvent. The result, however, due to the different composition of the two layers is a totally different layer dissolution speed, the effect of which is that the dissolution of the first layer, and the first cleansing stage defined hereby, are already terminated in the aforementioned one to three minutes, whereas the dissolution of the second layer and the related second cleansing stage become fully active only after this time, and are terminated only in approximately eight to twelve minutes, calculated from the time of introducing the two-layer tablet into the cleansing bath. Moreover, during dissolution of the first layer, as well as during dissolution of the second layer, the pH-value is set at 6.5 to 7.0.
The cleansing tablet according to German Offenlegungsschrift No. 2,357,720 has been proven entirely successful; however, it has been shown that the intended cleansing effect, given a predetermined percentage content of respective active agents, is still not entirely satisfactory for achieving self-acting cleansing of dentures in aqueous media.